Ultrasonic pulse-echo imaging systems are seeing increasing use in surgical procedures involving the insertion of a surgical instrument into the body for both the diagnosis and treatment of the body. One such procedure involves the obtaining of tissue samples by vacuum aspiration of the tissue through a hollow needle inserted into the body. Considerable efforts have been expended to provide accurate means for monitoring of the inserted instrument to avoid inadvertent tissue or organ puncture.
U.S. Pat. No. 4,249,539 outlines some of the difficulties encountered in monitoring the tip of the vacuum aspiration needles by use of either ultrasonic pulse-echo imaging or x-ray imaging. The solution proposed by U.S. Pat. No. 4,249,539 is the use of a second omnidirectional transducer at the tip of the needle or needle insert. Such a solution requires costly and complex electronics to be built into the needle or the needle insert. In addition, such a needle or needle insert cannot be autoclaved.
U.S. Pat. Nos. 3,556,079; 4,058,114; 4,029,084; and 3,721,227, involving method and apparatus for imaging the tip of an inserted needle or surgical instrument, may be fairly characterized as imposing highly restricted directional limitations on the inroduction of the needle or surgical instrument, whereby uncertainty and inaccuracy results. U.S. Pat. No. 3,556,079 discloses a method wherein organs or vessels which are in motion are irradiated and the backscattered waves exhibit a Doppler shift due to the motion of the organ or vessel.
This method has many drawbacks. In the method as depicted in FIG. 8a, the needle with transducer must be inserted in a direction such that it will encounter the anticipated Doppler shift to receive guidance in insertion. In the method depicted in FIGS. 8b and 8c, an external transducer as well as a transducer in the inserted needle must be disposed with respect to one another that the needle or the external transducer respectively encounters the anticipated Doppler shift.
U.S. Pat. Nos. 3,721,227 4,029,084; and 4,108,165 disclose systems wherein the first external transducer surrounds or encloses an opening through which a needle or surgical instrument may be directed and, which systems are therefor limited to the A-mode scanning technique which is not the preferred diagnostic approach due to the relatively small information content of its output.
U.S. Pat. No. 4,058,114 discloses an apparatus wherein the angle of insertion of the needle is disclosed by the external mechanical coupling for the needle; and an aiming pin disposed at the same angle as the external mechanical coupling of the needle overlies the visual picture of the ultrasound system providing only an imaginary overlay of the mechanical indicator and the electronic display.
U.S. Pat. No. 4,219,886 discloses a multipoint reflective target system for use as sonar targets. With the proper selection of the length of the sonar pulse, the spacing of the reflectors, and the size and material of the reflectors, the multipoint reflective target system can be made to resemble much larger, actual or simulated targets.